Geared turbofan gas turbine engine architecture

ABSTRACT

A gas turbine engine includes a combustor. A turbine section is in fluid communication with the combustor. The turbine section includes a fan drive turbine and a second turbine. The fan drive turbine includes a plurality of turbine rotors. A fan includes a plurality of blades rotatable about an axis and a ratio between the number of fan blades and the number of fan drive turbine rotors is between about 2.5 and about 8.5. A speed change system is driven by the fan drive turbine for rotating the fan about the axis. The fan drive turbine has a first exit area at a first exit point and rotates at a first speed. The second turbine section has a second exit area at a second exit point and rotates at a second speed, which is faster than the first speed. A first performance quantity is defined as the product of the first speed squared and the first area. A second performance quantity is defined as the product of the second speed squared and the second area. A performance ratio of the first performance quantity to the second performance quantity is between about 0.5 and about 1.5.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation in part of U.S. application Ser. No.14/609,909 filed on Jan. 30, 2015, which is a continuation in part ofU.S. application Ser. No. 13/645,665 filed on Oct. 5, 2012, which is acontinuation in part of U.S. application Ser. No. 13/363,154 filed onJan. 31, 2012 and claims priority to U.S. Provisional Application No.61/653,780 filed on May 31, 2012.

BACKGROUND

A gas turbine engine typically includes a fan section, a compressorsection, a combustor section and a turbine section. Air entering thecompressor section is compressed and delivered into the combustionsection where it is mixed with fuel and ignited to generate a high-speedexhaust gas flow. The high-speed exhaust gas flow expands through theturbine section to drive the compressor and the fan section. Thecompressor section typically includes low and high pressure compressors,and the turbine section includes low and high pressure turbines.

The high pressure turbine drives the high pressure compressor through anouter shaft to form a high spool, and the low pressure turbine drivesthe low pressure compressor through an inner shaft to form a low spool.The inner shaft may also drive the fan section. A direct drive gasturbine engine includes a fan section driven by the inner shaft suchthat the low pressure compressor, low pressure turbine and fan sectionrotate at a common speed in a common direction.

A speed reduction device such as an epicyclical gear assembly may beutilized to drive the fan section such that the fan section may rotateat a speed different than the turbine section so as to increase theoverall propulsive efficiency of the engine. In such enginearchitectures, a shaft driven by one of the turbine sections provides aninput to the epicyclical gear assembly that drives the fan section at aspeed different than the turbine section such that both the turbinesection and the fan section can rotate at closer to optimal speeds.

Although geared architectures have improved propulsive efficiency,turbine engine manufacturers continue to seek further improvements toengine performance including improvements to thermal, transfer andpropulsive efficiencies.

SUMMARY

In one exemplary embodiment, a gas turbine engine includes a combustor.A turbine section is in fluid communication with the combustor. Theturbine section includes a fan drive turbine and a second turbine. Thefan drive turbine includes a plurality of turbine rotors. A fan includesa plurality of blades rotatable about an axis and a ratio between thenumber of fan blades and the number of fan drive turbine rotors isbetween about 2.5 and about 8.5. A speed change system is driven by thefan drive turbine for rotating the fan about the axis. The fan driveturbine has a first exit area at a first exit point and rotates at afirst speed. The second turbine section has a second exit area at asecond exit point and rotates at a second speed, which is faster thanthe first speed. A first performance quantity is defined as the productof the first speed squared and the first area. A second performancequantity is defined as the product of the second speed squared and thesecond area. A performance ratio of the first performance quantity tothe second performance quantity is between about 0.5 and about 1.5.

In a further embodiment of the above, the first bearing assembly and thesecond bearing assembly include roller bearings.

In a further embodiment of any of the above, a compressor section thatincludes a first compressor driven by the fan drive turbine through thefirst shaft and a second compressor section driven by the second turbinethrough the second shaft. The first bearing supports an aft portion ofthe first shaft and the second bearing supports an aft portion of thesecond shaft.

In a further embodiment of any of the above, a forward portion of eachof the first and second shafts are supported by a thrust bearingassembly.

In a further embodiment of any of the above, the performance ratio isabove or equal to about 0.8.

In a further embodiment of any of the above, the speed change systemincludes a gearbox. The fan and the fan drive turbine both rotate in afirst direction about the axis and the second turbine section rotates ina second direction opposite the first direction.

In a further embodiment of any of the above, the speed change systemincludes a gearbox. The fan, the fan drive turbine section, and thesecond turbine section all rotate in a first direction about the axis.

In a further embodiment of any of the above, the speed change systemincludes a gearbox. The fan and the second turbine section both rotatein a first direction about the axis and the fan drive turbine rotates ina second direction opposite the first direction.

In a further embodiment of any of the above, the speed change systemincludes a gearbox. The fan is rotatable in a first direction and thefan drive turbine, and the second turbine section rotates in a seconddirection opposite the first direction about the axis.

In a further embodiment of any of the above, a fan pressure ratio acrossthe fan is less than about 1.5.

In a further embodiment of any of the above, the fan has 26 or fewerblades.

In a further embodiment of any of the above, fan drive turbine hasbetween about 3 and 6 stages.

In a further embodiment of any of the above, a pressure ratio across thefan drive turbine is greater than about 5:1.

In a further embodiment of any of the above, further including a thrustin pounds force (lbf) produced by the engine at a sea level take-offcondition and a volume (in³) of the turbine section. The thrust dividedby the turbine section volume is greater than about 1.5 lbf/in³ and lessthan or equal to about 5.5 lbf/in³.

In a further embodiment of any of the above, the second turbine includesat least two stages and performs at a first pressure ratio and the fandrive turbine includes more than two stages and performs at a secondpressure ratio less than the first pressure ratio.

In a further embodiment of any of the above, the fan drive turbineincludes a first aft rotor attached to a first shaft and the secondturbine includes a second aft rotor attached to a second shaft and afirst bearing assembly and a second bearing assembly are disposedaxially aft of the combustor with the first bearing assembly beingdisposed axially aft of a first connection between the first aft rotorand the first shaft, and the second bearing assembly being disposedaxially forward of a second connection between the second aft rotor andthe second shaft.

In a further embodiment of any of the above, the fan drive turbine isone of three turbine rotors. The fan drive turbine drives the fan. Theother of the turbine rotors each drive a compressor rotor of acompressor section.

In a further embodiment of any of the above, the speed change system ispositioned intermediate a compressor rotor and a shaft driven by the fandrive turbine.

Although the different examples have the specific components shown inthe illustrations, embodiments of this disclosure are not limited tothose particular combinations. It is possible to use some of thecomponents or features from one of the examples in combination withfeatures or components from another one of the examples.

These and other features disclosed herein can be best understood fromthe following specification and drawings, the following of which is abrief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an example gas turbine engine.

FIG. 2 is a schematic view indicating relative rotation between sectionsof an example gas turbine engine.

FIG. 3 is another schematic view indicating relative rotation betweensections of an example gas turbine engine.

FIG. 4 is another schematic view indicating relative rotation betweensections of an example gas turbine engine.

FIG. 5 is another a schematic view indicating relative rotation betweensections of an example gas turbine engine.

FIG. 6 is a schematic view of a bearing configuration supportingrotation of example high and low spools of the example gas turbineengine.

FIG. 7 is another schematic view of a bearing configuration supportingrotation of example high and low spools of the example gas turbineengine.

FIG. 8A is another schematic view of a bearing configuration supportingrotation of example high and low spools of the example gas turbineengine.

FIG. 8B is an enlarged view of the example bearing configuration shownin FIG. 8A.

FIG. 9 is another schematic view of a bearing configuration supportingrotation of example high and low spools of the example gas turbineengine.

FIG. 10 is a schematic view of an example compact turbine section.

FIG. 11 is a schematic cross-section of example stages for the disclosedexample gas turbine engine.

FIG. 12 is a schematic view an example turbine rotor perpendicular tothe axis or rotation.

FIG. 13 is another embodiment of an example gas turbine engine for usewith the present invention.

FIG. 14 is yet another embodiment of an example gas turbine engine foruse with the present invention.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates an example gas turbine engine 20 thatincludes a fan section 22, a compressor section 24, a combustor section26 and a turbine section 28. Alternative engines might include anaugmenter section (not shown) among other systems or features. The fansection 22 drives air along a bypass flow path B while the compressorsection 24 draws air in along a core flow path C where air is compressedand communicated to a combustor section 26. In the combustor section 26,air is mixed with fuel and ignited to generate a high pressure exhaustgas stream that expands through the turbine section 28 where energy isextracted and utilized to drive the fan section 22 and the compressorsection 24.

Although the disclosed non-limiting embodiment depicts a turbofan gasturbine engine, it should be understood that the concepts describedherein are not limited to use with turbofans as the teachings may beapplied to other types of turbine engines; for example a turbine engineincluding a three-spool architecture in which three spoolsconcentrically rotate about a common axis such that a low spool enablesa low pressure turbine to drive a fan via a gearbox, an intermediatespool enables an intermediate pressure turbine to drive a firstcompressor of the compressor section, and a high spool enables a highpressure turbine to drive a high pressure compressor of the compressorsection.

The example engine 20 generally includes a low speed spool 30 and a highspeed spool 32 mounted for rotation about an engine central longitudinalaxis A relative to an engine static structure 36 via several bearingsystems 38. It should be understood that various bearing systems 38 atvarious locations may alternatively or additionally be provided.

The low speed spool 30 generally includes an inner shaft 40 thatconnects a fan 42 and a low pressure (or first) compressor section 44 toa low pressure (or first) turbine section 46. The inner shaft 40 drivesthe fan 42 through a speed change device, such as a geared architecture48, to drive the fan 42 at a lower speed than the low speed spool 30.The high-speed spool 32 includes an outer shaft 50 that interconnects ahigh pressure (or second) compressor section 52 and a high pressure (orsecond) turbine section 54. The inner shaft 40 and the outer shaft 50are concentric and rotate via the bearing systems 38 about the enginecentral longitudinal axis A.

A combustor 56 is arranged between the high pressure compressor 52 andthe high pressure turbine 54. In one example, the high pressure turbine54 includes at least two stages to provide a double stage high pressureturbine 54. In another example, the high pressure turbine 54 includesonly a single stage. As used herein, a “high pressure” compressor orturbine experiences a higher pressure than a corresponding “lowpressure” compressor or turbine.

The example low pressure turbine 46 has a pressure ratio that is greaterthan about 5. The pressure ratio of the example low pressure turbine 46is measured prior to an inlet of the low pressure turbine 46 as relatedto the pressure measured at the outlet of the low pressure turbine 46prior to an exhaust nozzle.

A mid-turbine frame 58 of the engine static structure 36 is arrangedgenerally between the high pressure turbine 54 and the low pressureturbine 46. The mid-turbine frame 58 further supports bearing systems 38in the turbine section 28 as well as setting airflow entering the lowpressure turbine 46.

The core airflow C is compressed by the low pressure compressor 44 thenby the high pressure compressor 52 mixed with fuel and ignited in thecombustor 56 to produce high speed exhaust gases that are then expandedthrough the high pressure turbine 54 and low pressure turbine 46. Themid-turbine frame 58 includes vanes 60, which are in the core airflowpath and function as an inlet guide vane for the low pressure turbine46. Utilizing the vane 60 of the mid-turbine frame 58 as the inlet guidevane for low pressure turbine 46 decreases the length of the lowpressure turbine 46 without increasing the axial length of themid-turbine frame 58. Reducing or eliminating the number of vanes in thelow pressure turbine 46 shortens the axial length of the turbine section28. Thus, the compactness of the gas turbine engine 20 is increased anda higher power density may be achieved.

The disclosed gas turbine engine 20 in one example is a high-bypassgeared aircraft engine. In a further example, the gas turbine engine 20includes a bypass ratio greater than about six (6), with an exampleembodiment being greater than about ten (10). The example gearedarchitecture 48 is an epicyclical gear train, such as a planetary gearsystem, star gear system or other known gear system, with a gearreduction ratio of greater than about 2.3.

In one disclosed embodiment, the gas turbine engine 20 includes a bypassratio greater than about ten (10:1) and the fan diameter issignificantly larger than an outer diameter of the low pressurecompressor 44. It should be understood, however, that the aboveparameters are only exemplary of one embodiment of a gas turbine engineincluding a geared architecture and that the present disclosure isapplicable to other gas turbine engines.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft., withthe engine at its best cruise fuel consumption relative to the thrust itproduces—also known as “bucket cruise Thrust Specific Fuel Consumption(‘TSFCT’)” is the industry standard parameter of pound-mass (lbm) offuel per hour being burned divided by pound-force (lbf) of thrust theengine produces at that minimum bucket cruise point.

“Low fan pressure ratio” is the pressure ratio across the fan bladealone, without a Fan Exit Guide Vane (“FEGV”) system. The low fanpressure ratio as disclosed herein according to one non-limitingembodiment is less than about 1.50. In another non-limiting embodimentthe low fan pressure ratio is less than about 1.45.

“Low corrected fan tip speed” is the actual fan tip speed in ft/secdivided by an industry standard temperature correction of [(Tram°R)/518.7)^(0.5)]. The “Low corrected fan tip speed”, as disclosedherein according to one non-limiting embodiment, is less than about 1150ft/second.

The example gas turbine engine includes the fan 42 that comprises in onenon-limiting embodiment less than about 26 fan blades. In anothernon-limiting embodiment, the fan section 22 includes less than about 18fan blades. Moreover, in one disclosed embodiment the low pressureturbine 46 includes no more than about 6 turbine stages schematicallyindicated at 34. In another non-limiting example embodiment the lowpressure turbine 46 includes about 3 or more turbine stages. A ratiobetween the number of fan blades 42 and the number of low pressureturbine stages is between about 2.5 and about 8.5. The example lowpressure turbine 46 provides the driving power to rotate the fan section22 and therefore the relationship between the number of turbine stages34 in the low pressure turbine 46 and the number of blades 42 in the fansection 22 disclose an example gas turbine engine 20 with increasedpower transfer efficiency.

Increased power transfer efficiency is provided due in part to theincreased use of improved turbine blade materials and manufacturingmethods such as directionally solidified castings, and single crystalmaterials that enable increased turbine speed and a reduced number ofstages. Moreover, the example low pressure turbine 46 includes improvedturbine disks configurations that further enable desired durability atthe higher turbine speeds.

Referring to FIGS. 2 and 3, an example disclosed speed change device isan epicyclical gearbox of a planet type, where the input is to thecenter “sun” gear 62. Planet gears 64 (only one shown) around the sungear 62 rotate and are spaced apart by a carrier 68 that rotates in adirection common to the sun gear 62. A ring gear 66, which isnon-rotatably fixed to the engine static casing 36 (shown in FIG. 1),contains the entire gear assembly. The fan 42 is attached to and drivenby the carrier 68 such that the direction of rotation of the fan 42 isthe same as the direction of rotation of the carrier 68 that, in turn,is the same as the direction of rotation of the input sun gear 62.

In the following figures nomenclature is utilized to define the relativerotations between the various sections of the gas turbine engine 20. Thefan section is shown with a “+” sign indicating rotation in a firstdirection. Rotations relative to the fan section 22 of other features ofthe gas turbine engine are further indicated by the use of either a “+”sign or a “−” sign. The “−” sign indicates a rotation that is counter tothat of any component indicated with a “+” sign.

Moreover, the term fan drive turbine is utilized to indicate the turbinethat provides the driving power for rotating the blades 42 of the fansection 22. Further, the term “second turbine” is utilized to indicatethe turbine before the fan drive turbine that is not utilized to drivethe fan 42. In this disclosed example, the fan drive turbine is the lowpressure turbine 46, and the second turbine is the high pressure turbine54. However, it should be understood that other turbine sectionconfigurations that include more than the shown high and low pressureturbines 54, 46 are within the contemplation of this disclosure. Forexample, a three spool engine configuration may include an intermediateturbine (not shown) utilized to drive the fan section 22 and is withinthe contemplation of this disclosure.

In one disclosed example embodiment (FIG. 2) the fan drive turbine isthe low pressure turbine 46 and therefore the fan section 22 and lowpressure turbine 46 rotate in a common direction as indicated by thecommon “+” sign indicating rotation of both the fan 42 and the lowpressure turbine 46. Moreover in this example, the high pressure turbine54 or second turbine rotates in a direction common with the fan driveturbine 46. In another example shown in FIG. 3, the high pressureturbine 54 or second turbine rotates in a direction opposite the fandrive turbine (low pressure turbine 46) and the fan 42.

Counter rotating the low pressure compressor 44 and the low pressureturbine 46 relative to the high pressure compressor 52 and the highpressure turbine 54 provides certain efficient aerodynamic conditions inthe turbine section 28 as the generated high speed exhaust gas flowmoves from the high pressure turbine 54 to the low pressure turbine 46.The relative rotations in the compressor and turbine sections provideapproximately the desired airflow angles between the sections, whichimprove overall efficiency in the turbine section 28, and provide areduction in overall weight of the turbine section 28 by reducing oreliminating airfoils or an entire row of vanes.

Referring to FIGS. 4 and 5, another example disclosed speed changedevice is an epicyclical gearbox referred to as a star type gearbox,where the input is to the center “sun” gear 62. Star gears 65 (only oneshown) around the sun gear 62 rotate in a fixed position around the sungear and are spaced apart by a carrier 68 that is fixed to a staticcasing 36 (best shown in FIG. 1). A ring gear 66 that is free to rotatecontains the entire gear assembly. The fan 42 is attached to and drivenby the ring gear 66 such that the direction of rotation of the fan 42 isopposite the direction of rotation of the input sun gear 62.Accordingly, the low pressure compressor 44 and the low pressure turbine46 rotate in a direction opposite rotation of the fan 42.

In one disclosed example embodiment shown in FIG. 4, the fan driveturbine is the low pressure turbine 46 and therefore the fan 42 rotatesin a direction opposite that of the low pressure turbine 46 and the lowpressure compressor 44. Moreover in this example the high spool 32including the high pressure turbine 54 and the high pressure compressor52 rotate in a direction counter to the fan 42 and common with the lowspool 30 including the low pressure compressor 44 and the fan driveturbine 46.

In another example gas turbine engine shown in FIG. 5, the high pressureor second turbine 54 rotates in a direction common with the fan 42 andcounter to the low spool 30 including the low pressure compressor 44 andthe fan drive turbine 46.

Referring to FIG. 6, the bearing assemblies near the forward end of theshafts in the engine at locations 70 and 72, which bearings supportrotation of the inner shaft 40 and the outer shaft 50, counter netthrust forces in a direction parallel to the axis A that are generatedby the rearward load of low pressure turbine 46 and the high pressureturbine 54, minus the high pressure compressor 52 and the low pressurecompressor 44, which also contribute to the thrust forces acting on thecorresponding low spool 30 and the high spool 32.

In this example embodiment, a first forward bearing assembly 70 issupported on a portion of the static structure schematically shown at 36and supports a forward end of the inner shaft 40. The example firstforward bearing assembly 70 is a thrust bearing and controls movement ofthe inner shaft 40 and thereby the low spool 30 in an axial direction. Asecond forward bearing assembly 72 is supported by the static structure36 to support rotation of the high spool 32 and substantially preventmovement along in an axial direction of the outer shaft 50. The firstforward bearing assembly 70 is mounted to support the inner shaft 40 ata point forward of a connection 88 of a low pressure compressor rotor90. The second forward bearing assembly 72 is mounted forward of aconnection referred to as a hub 92 between a high pressure compressorrotor 94 and the outer shaft 50. A first aft bearing assembly 74supports the aft portion of the inner shaft 40. The first aft bearingassembly 74 is a roller bearing and supports rotation, but does notprovide resistance to movement of the shaft 40 in the axial direction.Instead, the aft bearing 74 allows the shaft 40 to expand thermallybetween its location and the bearing 72. The example first aft bearingassembly 74 is disposed aft of a connection hub 80 between a lowpressure turbine rotor 78 and the inner shaft 40. A second aft bearingassembly 76 supports the aft portion of the outer shaft 50. The examplesecond aft bearing assembly 76 is a roller bearing and is supported by acorresponding static structure 36 through the mid turbine frame 58 whichtransfers the radial load of the shaft across the turbine flow path toground 36. The second aft bearing assembly 76 supports the outer shaft50 and thereby the high spool 32 at a point aft of a connection hub 84between a high pressure turbine rotor 82 and the outer shaft 50.

In this disclosed example, the first and second forward bearingassemblies 70, 72 and the first and second aft bearing assemblies 74, 76are supported to the outside of either the corresponding compressor orturbine connection hubs 80, 88 to provide a straddle supportconfiguration of the corresponding inner shaft 40 and outer shaft 50.The straddle support of the inner shaft 40 and the outer shaft 50provide a support and stiffness desired for operation of the gas turbineengine 20.

Referring to FIG. 7, another example shaft support configurationincludes the first and second forward bearing assemblies 70, 72 disposedto support the forward portion of the corresponding inner shaft 40 andouter shaft 50. The first aft bearing 74 is disposed aft of theconnection 80 between the rotor 78 and the inner shaft 40. The first aftbearing 74 is a roller bearing and supports the inner shaft 40 in astraddle configuration. The straddle configuration can requireadditional length of the inner shaft 40 and therefore an alternateconfiguration referred to as an overhung configuration can be utilized.In this example the outer shaft 50 is supported by the second aftbearing assembly 76 that is disposed forward of the connection 84between the high pressure turbine rotor 82 and the outer shaft 50.Accordingly, the connection hub 84 of the high pressure turbine rotor 82to the outer shaft 50 is overhung aft of the bearing assembly 76. Thispositioning of the second aft bearing 76 in an overhung orientationpotentially provides for a reduced length of the outer shaft 50.

Moreover the positioning of the aft bearing 76 may also eliminate theneed for other support structures such as the mid turbine frame 58 asboth the high pressure turbine 54 is supported at the bearing assembly76 and the low pressure turbine 46 is supported by the bearing assembly74. Optionally the mid turbine frame strut 58 can provide an optionalroller bearing 74A which can be added to reduce vibratory modes of theinner shaft 40.

Referring to FIGS. 8A and 8B, another example shaft supportconfiguration includes the first and second forward bearing assemblies70, 72 disposed to support corresponding forward portions of each of theinner shaft 40 and the outer shaft 50. The first aft bearing 74 providessupport of the outer shaft 40 at a location aft of the connection 80 ina straddle mount configuration. In this example, the aft portion of theouter shaft 50 is supported by a roller bearing assembly 86 supportedwithin a space 96 defined between an outer surface of the inner shaft 40and an inner surface of the outer shaft 50.

The roller bearing assembly 86 supports the aft portion of the outershaft 50 on the inner shaft 40. The use of the roller bearing assembly86 to support the outer shaft 50 eliminates the requirements for supportstructures that lead back to the static structure 36 through the midturbine frame 58. Moreover, the example bearing assembly 86 can provideboth a reduced shaft length, and support of the outer shaft 50 at aposition substantially in axial alignment with the connection hub 84 forthe high pressure turbine rotor 82 and the outer shaft 50. Asappreciated, the bearing assembly 86 is positioned aft of the hub 82 andis supported through the rearmost section of shaft 50. Referring to FIG.9, another example shaft support configuration includes the first andsecond forward bearing assemblies 70, 72 disposed to supportcorresponding forward portions of each of the inner shaft 40 and theouter shaft 50. The first aft bearing assembly 74 is supported at apoint along the inner shaft 40 forward of the connection 80 between thelow pressure turbine rotor 78 and the inner shaft 40.

Positioning of the first aft bearing 74 forward of the connection 80 canbe utilized to reduce the overall length of the engine 20. Moreover,positioning of the first aft bearing assembly 74 forward of theconnection 80 provides for support through the mid turbine frame 58 tothe static structure 36. Furthermore, in this example the second aftbearing assembly 76 is deployed in a straddle mount configuration aft ofthe connection 84 between the outer shaft 50 and the rotor 82.Accordingly, in this example, both the first and second aft bearingassemblies 74, 76 share a common support structure to the static outerstructure 36. As appreciated, such a common support feature provides fora less complex engine construction along with reducing the overalllength of the engine. Moreover, the reduction or required supportstructures will reduce overall weight to provide a further improvementin aircraft fuel burn efficiency.

Referring to FIG. 10, a portion of the example turbine section 28 isshown and includes the low pressure turbine 46 and the high pressureturbine 54 with the mid turbine frame 58 disposed between an outlet ofthe high pressure turbine and the low pressure turbine. The mid turbineframe 58 and vane 60 are positioned to be upstream of the first stage 98of the low pressure turbine 46. While a single vane 60 is illustrated,it should be understood these would be plural vanes 60 spacedcircumferentially. The vane 60 redirects the flow downstream of the highpressure turbine 54 as it approaches the first stage 98 of the lowpressure turbine 46. As can be appreciated, it is desirable to improveefficiency to have flow between the high pressure turbine 54 and the lowpressure turbine 46 redirected by the vane 60 such that the flow ofexpanding gases is aligned as desired when entering the low pressureturbine 46. Therefore vane 60 may be an actual airfoil with camber andturning, that aligns the airflow as desired into the low pressureturbine 46.

By incorporating a true air-turning vane 60 into the mid turbine frame58, rather than a streamlined strut and a stator vane row after thestrut, the overall length and volume of the combined turbine sections46, 54 is reduced because the vane 60 serves several functions includingstreamlining the mid turbine frame 58, protecting any static structureand any oil tubes servicing a bearing assembly from exposure to heat,and turning the flow entering the low pressure turbine 46 such that itenters the rotating airfoil 100 at a desired flow angle. Further, byincorporating these features together, the overall assembly andarrangement of the turbine section 28 is reduced in volume.

The above features achieve a more or less compact turbine section volumerelative to the prior art including both high and low pressure turbines54, 46. Moreover, in one example, the materials for forming the lowpressure turbine 46 can be improved to provide for a reduced volume.Such materials may include, for example, materials with increasedthermal and mechanical capabilities to accommodate potentially increasedstresses induced by operating the low pressure turbine 46 at theincreased speed. Furthermore, the elevated speeds and increasedoperating temperatures at the entrance to the low pressure turbine 46enables the low pressure turbine 46 to transfer a greater amount ofenergy, more efficiently to drive both a larger diameter fan 42 throughthe geared architecture 48 and an increase in compressor work performedby the low pressure compressor 44.

Alternatively, lower priced materials can be utilized in combinationwith cooling features that compensate for increased temperatures withinthe low pressure turbine 46. In three exemplary embodiments a firstrotating blade 100 of the low pressure turbine 46 can be a directionallysolidified casting blade, a single crystal casting blade or a hollow,internally cooled blade. The improved material and thermal properties ofthe example turbine blade material provide for operation at increasedtemperatures and speeds, that in turn provide increased efficiencies ateach stage that thereby provide for use of a reduced number of lowpressure turbine stages. The reduced number of low pressure turbinestages in turn provide for an overall turbine volume that is reduced,and that accommodates desired increases in low pressure turbine speed.

The reduced stages and reduced volume provide improve engine efficiencyand aircraft fuel burn because overall weight is less. In addition, asthere are fewer blade rows, there are: fewer leakage paths at the tipsof the blades; fewer leakage paths at the inner air seals of vanes; andreduced losses through the rotor stages.

The example disclosed compact turbine section includes a power density,which may be defined as thrust in pounds force (lbf) produced divided bythe volume of the entire turbine section 28. The volume of the turbinesection 28 may be defined by an inlet 102 of a first turbine vane 104 inthe high pressure turbine 54 to the exit 106 of the last rotatingairfoil 108 in the low pressure turbine 46, and may be expressed incubic inches. The static thrust at the engine's flat rated Sea LevelTakeoff condition divided by a turbine section volume is defined aspower density and a greater power density may be desirable for reducedengine weight. The sea level take-off flat-rated static thrust may bedefined in pounds-force (lbf), while the volume may be the volume fromthe annular inlet 102 of the first turbine vane 104 in the high pressureturbine 54 to the annular exit 106 of the downstream end of the lastairfoil 108 in the low pressure turbine 46. The maximum thrust may beSea Level Takeoff Thrust “SLTO thrust” which is commonly defined as theflat-rated static thrust produced by the turbofan at sea-level.

The volume V of the turbine section may be best understood from FIG. 10.As shown, the mid turbine frame 58 is disposed between the high pressureturbine 54, and the low pressure turbine 46. The volume V is illustratedby a dashed line, and extends from an inner periphery I to an outerperiphery O. The inner periphery is defined by the flow path of rotors,but also by an inner platform flow paths of vanes. The outer peripheryis defined by the stator vanes and outer air seal structures along theflowpath. The volume extends from a most upstream end of the vane 104,typically its leading edge, and to the most downstream edge of the lastrotating airfoil 108 in the low pressure turbine section 46. Typicallythis will be the trailing edge of the airfoil 108.

The power density in the disclosed gas turbine engine is much higherthan in the prior art. Eight exemplary engines are shown below whichincorporate turbine sections and overall engine drive systems andarchitectures as set forth in this application, and can be found inTable I as follows:

TABLE 1 Thrust SLTO Turbine section volume Thrust/turbine section Engine(lbf) from the Inlet volume (lbf/in³) 1 17,000 3,859 4.40 2 23,300 5,3304.37 3 29,500 6,745 4.37 4 33,000 6,745 4.84 5 96,500 31,086 3.10 696,500 62,172 1.55 7 96,500 46,629 2.07 8 37,098 6,745 5.50

Thus, in example embodiments, the power density would be greater than orequal to about 1.5 lbf/in³. More narrowly, the power density would begreater than or equal to about 2.0 lbf/in³. Even more narrowly, thepower density would be greater than or equal to about 3.0 lbf/in³. Morenarrowly, the power density is greater than or equal to about 4.0lbf/in³. Also, in embodiments, the power density is less than or equalto about 5.5 lbf/in³.

Engines made with the disclosed architecture, and including turbinesections as set forth in this application, and with modifications withinthe scope of this disclosure, thus provide very high efficientoperation, and increased fuel efficiency and lightweight relative totheir thrust capability.

An exit area 112 is defined at the exit location for the high pressureturbine 54 and an exit area 110 is defined at the outlet 106 of the lowpressure turbine 46. The gear reduction 48 (shown in FIG. 1) providesfor a range of different rotational speeds of the fan drive turbine,which in this example embodiment is the low pressure turbine 46, and thefan 42 (FIG. 1). Accordingly, the low pressure turbine 46, and therebythe low spool 30 including the low pressure compressor 44 may rotate ata very high speed. Low pressure turbine 46 and high pressure turbine 54operation may be evaluated looking at a performance quantity which isthe exit area for the respective turbine section multiplied by itsrespective speed squared. This performance quantity (“PQ”) is definedas:

PQ_(ltp)=(A _(lpt) ×V _(lpt) ²)  Equation 1:

PQ_(hpt)=(A _(hpt) ×V _(hpt) ²)  Equation 2:

where A_(lpt) is the area 110 of the low pressure turbine 46 at the exit106, V_(lpt) is the speed of the low pressure turbine section; A_(hpt)is the area of the high pressure turbine 54 at the exit 114, and whereV_(hpt) is the speed of the high pressure turbine 54.

Thus, a ratio of the performance quantity for the low pressure turbine46 compared to the performance quantify for the high pressure turbine 54is:

(A _(lpt) ×V _(lpt) ²)/(A _(hpt) ×V _(hpt)²)=PQ_(ltp)/PQ_(htp)  Equation 3:

In one turbine embodiment made according to the above design, the areasof the low and high pressure turbines 46, 54 are 557.9 in² and 90.67in², respectively. Further, the speeds of the low and high pressureturbine 46, 54 are 10179 rpm and 24346 rpm, respectively. Thus, usingEquations 1 and 2 above, the performance quantities for the example lowand high pressure turbines 46,54 are:

PQ_(ltp)=(A _(ltp) ×V _(lpt) ²)=(557.9 in²)(10179 rpm)²=57805157673.9in² rpm²  Equation 1:

PQ_(hpt)=(A _(hpt) ×V _(hpt) ²)=(90.67 in²)(24346 rpm)²=53742622009.72in² rpm²  Equation 2:

and using Equation 3 above, the ratio for the low pressure turbinesection to the high pressure turbine section is:

Ratio=PQ_(ltp)/PQ_(hpt)=57805157673.9 in² rpm²/53742622009.72 in²rpm²=1.075

In another embodiment, the ratio is greater than about 0.5 and inanother embodiment the ratio is greater than about 0.8. WithPQ_(ltp)/PQ_(hpt) ratios in the 0.5 to 1.5 range, a very efficientoverall gas turbine engine is achieved. More narrowly, PQ_(ltp)/PQ_(hpt)ratios of above or equal to about 0.8 provides increased overall gasturbine efficiency. Even more narrowly, PQ_(ltp)/PQ_(hpt) ratios aboveor equal to 1.0 are even more efficient thermodynamically and from anenable a reduction in weight that improves aircraft fuel burnefficiency. As a result of these PQ_(ltp)/PQ_(hpt) ratios, inparticular, the turbine section 28 can be made much smaller than in theprior art, both in diameter and axial length. In addition, theefficiency of the overall engine is greatly increased.

Referring to FIG. 11, portions of the low pressure compressor 44 and thelow pressure turbine 46 of the low spool 30 are schematically shown andinclude rotors 116 of the low pressure turbine 46 and rotors 132 of thelow pressure compressor 44. Each of the rotors 116 includes a boreradius 122, a live disk radius 124 and a bore width 126 in a directionparallel to the axis A. The rotor 116 supports turbine blades 118 thatrotate relative to the turbine vanes 120. The low pressure compressor 44includes rotors 132 including a bore radius 134, a live disk radius 136and a bore width 138. The rotor 132 supports compressor blades 128 thatrotate relative to vanes 130.

The bore radius 122 is that radius between an inner most surface of thebore and the axis. The live disk radius 124 is the radial distance fromthe axis of rotation A and a portion of the rotor supporting airfoilblades. The bore width 126 of the rotor in this example is the greatestwidth of the rotor and is disposed at a radial distance spaced apartfrom the axis A determined to provide desired physical performanceproperties.

The rotors for each of the low compressor 44 and the low pressureturbine 46 rotate at an increased speed compared to prior art low spoolconfigurations. The geometric shape including the bore radius, live diskradius and the bore width are determined to provide the desired rotorperformance in view of the mechanical and thermal stresses selected tobe imposed during operation. Referring to FIG. 12, with continuedreference to FIG. 11, a turbine rotor 116 is shown to further illustratethe relationship between the bore radius 126 and the live disk radius124. Moreover, the relationships disclosed are provided within a knownrange of materials commonly utilized for construction of each of therotors.

Accordingly, the increased performance attributes and performance areprovided by desirable combinations of the disclosed features of thevarious components of the described and disclosed gas turbine engineembodiments.

FIG. 13 shows an embodiment 200, wherein there is a fan drive turbine208 driving a shaft 206 to in turn drive a fan rotor 202. A gearreduction 204 may be positioned between the fan drive turbine 208 andthe fan rotor 202. This gear reduction 204 may be structured and operatelike the gear reduction disclosed above. A compressor rotor 210 isdriven by an intermediate pressure turbine 212, and a second stagecompressor rotor 214 is driven by a turbine rotor 216. A combustionsection 218 is positioned intermediate the compressor rotor 214 and theturbine section 216.

FIG. 14 shows yet another embodiment 300 wherein a fan rotor 302 and afirst stage compressor 304 rotate at a common speed. The gear reduction306 (which may be structured as disclosed above) is intermediate thecompressor rotor 304 and a shaft 308 which is driven by a low pressureturbine section.

The embodiments 200, 300 of FIG. 13 or 14 may be utilized with thefeatures disclosed above.

Although an example embodiment has been disclosed, a worker of ordinaryskill in this art would recognize that certain modifications would comewithin the scope of this disclosure. For that reason, the followingclaims should be studied to determine the scope and content of thisdisclosure.

What is claimed is:
 1. A gas turbine engine comprising: a combustor; aturbine section in fluid communication with the combustor, the turbinesection including a fan drive turbine and a second turbine, the fandrive turbine including a plurality of turbine rotors; a fan including aplurality of blades rotatable about an axis and a ratio between thenumber of fan blades and the number of fan drive turbine rotors isbetween about 2.5 and about 8.5; and a speed change system driven by thefan drive turbine for rotating the fan about the axis; wherein the fandrive turbine has a first exit area at a first exit point and rotates ata first speed, the second turbine section has a second exit area at asecond exit point and rotates at a second speed, which is faster thanthe first speed, wherein a first performance quantity is defined as theproduct of the first speed squared and the first area, a secondperformance quantity is defined as the product of the second speedsquared and the second area, and a performance ratio of the firstperformance quantity to the second performance quantity is between about0.5 and about 1.5.
 2. The engine as recited in claim 2, wherein thefirst bearing assembly and the second bearing assembly comprise rollerbearings.
 3. The engine as recited in claim 2, including a compressorsection that comprises a first compressor driven by the fan driveturbine through the first shaft and a second compressor section drivenby the second turbine through the second shaft, wherein the firstbearing supports an aft portion of the first shaft and the secondbearing supports an aft portion of the second shaft.
 4. The engine asrecited in claim 3, wherein a forward portion of each of the first andsecond shafts are supported by a thrust bearing assembly.
 5. The engineas recited in claim 1, wherein the performance ratio is above or equalto about 0.8.
 6. The engine as recited in claim 1, wherein the speedchange system comprises a gearbox, and wherein the fan and the fan driveturbine both rotate in a first direction about the axis and the secondturbine section rotates in a second direction opposite the firstdirection.
 7. The engine as recited in claim 1, wherein the speed changesystem comprises a gearbox, and wherein the fan, the fan drive turbinesection, and the second turbine section all rotate in a first directionabout the axis.
 8. The engine as recited in claim 1, wherein the speedchange system comprises a gearbox, and wherein the fan and the secondturbine section both rotate in a first direction about the axis and thefan drive turbine rotates in a second direction opposite the firstdirection.
 9. The engine as recited in claim 1, wherein the speed changesystem comprises a gearbox, and wherein the fan is rotatable in a firstdirection and the fan drive turbine, and the second turbine sectionrotates in a second direction opposite the first direction about theaxis.
 10. The engine as recited in claim 1, wherein a fan pressure ratioacross the fan is less than about 1.5.
 11. The engine as recited inclaim 1, wherein the fan has 26 or fewer blades.
 12. The engine asrecited in claim 1, wherein fan drive turbine has between about 3 and 6stages.
 13. The engine as recited in claim 1, wherein a pressure ratioacross the fan drive turbine is greater than about 5:1.
 14. The engineas recited in claim 1, further comprising: a thrust in pounds force(lbf) produced by the engine at a sea level take-off condition; and avolume (in³) of the turbine section, wherein the thrust divided by theturbine section volume is greater than about 1.5 lbf/in³ and less thanor equal to about 5.5 lbf/in³.
 15. The engine as recited in claim 1,wherein the second turbine includes at least two stages and performs ata first pressure ratio and the fan drive turbine includes more than twostages and performs at a second pressure ratio less than the firstpressure ratio.
 16. The engine as recited in claim 1, wherein the fandrive turbine includes a first aft rotor attached to a first shaft andthe second turbine includes a second aft rotor attached to a secondshaft and a first bearing assembly and a second bearing assembly aredisposed axially aft of the combustor with the first bearing assemblybeing disposed axially aft of a first connection between the first aftrotor and the first shaft, and the second bearing assembly beingdisposed axially forward of a second connection between the second aftrotor and the second shaft.
 17. The engine as recited in claim 1,wherein the fan drive turbine is one of three turbine rotors, the fandrive turbine driving the fan, the other of the turbine rotors eachdriving a compressor rotor of a compressor section.
 18. The engine asrecited in claim 1, wherein the speed change system is positionedintermediate a compressor rotor and a shaft driven by the fan driveturbine.